SDHB-Deficient Cancers: The Role of Mutations That Impair Iron Sulfur Cluster Delivery

Background: Mutations in the Fe-S cluster-containing SDHB subunit of succinate dehydrogenase cause familial cancer syndromes. Recently the tripeptide motif L(I)YR was identified in the Fe-S recipient protein SDHB, to which the cochaperone HSC20 binds. Methods: In order to characterize the metabolic basis of SDH-deficient cancers we performed stable isotope-resolved metabolomics in a novel SDHB-deficient renal cell carcinoma cell line and conducted bioinformatics and biochemical screening to analyze Fe-S cluster acquisition and assembly of SDH in the presence of other cancer-causing SDHB mutations. Results: We found that the SDHBR46Q mutation in UOK269 cells disrupted binding of HSC20, causing rapid degradation of SDHB. In the absence of SDHB, respiration was undetectable in UOK269 cells, succinate was elevated to 351.4 +/- 63.2 nmol/mg cellular protein, and glutamine became the main source of TCA cycle metabolites through reductive carboxylation. Furthermore, HIF1 alpha, but not HIF2 alpha, increased markedly and the cells showed a strong DNA CpG island methylator phenotype (CIMP). Biochemical and bioinformatic screening revealed that 37% of disease-causing missense mutations in SDHB were located in either the L(I)YR Fe-S transfer motifs or in the 11 Fe-S cluster-ligating cysteines. Conclusions: These findings provide a conceptual framework for understanding how particular mutations disproportionately cause the loss of SDH activity, resulting in accumulation of succinate and metabolic remodeling in SDHB cancer syndromes.